1. Field of the Invention
The present invention relates to a semiconductor device including a semiconductor chip having a back surface bonded to a heat dissipation plate.
2. Description of the Related Art
FIG. 9 shows a conventional BGA (ball grid array) semiconductor device including a metal plate 100 of a copper, aluminum, or other highly heat-conductive metal and a semiconductor chip 102 having a back surface bonded to a lower surface of the metal plate 100 with an adhesive layer 103. Electrode terminals 104 are formed on an active surface, opposite to the back surface, of the semiconductor chip 102 and are flip-chip bonded to first ends of conductor patterns 108 formed on an upper surface of a flexible circuit substrate 106.
The flexible circuit substrate 106 is composed a flexible resin film 110 of polyimide or other electrically insulating resin, conductor patterns 108 are formed on one surface of the substrate 106, external connection terminals or solder balls 112 are formed on second ends of the conductor patterns 108 and downwardly extend through the resin film 110 via through holes 111 via through holes 111 of the resin film 110 to protrude from a lower surface of the resin film 110. The flexible circuit substrate 106, the metal plate 100 and the semiconductor chip 102 are bonded together with an adhesive layer 114.
The metal plate 100 has an area larger than that of the semiconductor chip 102. The external connection terminals or solder balls 112 are located between a periphery of the semiconductor chip 102 and a periphery of the metal plate 100. The conductor patterns 108 are bonded to the metal plate 100 with the adhesive layer 114 and provide electrical connection from the electrode terminals 104 to the solder balls 112. The metal plate 100 provides thermal dissipation and a direct support for the flexible circuit substrate 106, and in turn, an indirect support for the solder balls 112 and the conductor patterns 108.
The BGA semiconductor device shown in FIG. 9 provides a reduction in cost and fine conductor patterns in comparison with prior BGA types.
However, problems arise with the recent trend of a reduction in the thickness of the semiconductor chip 102 to as small as 100 xcexcm or less.
The external connection terminals or solder balls 112 are supported by the flexible circuit substrate 106 while being located between a periphery of the semiconductor chip 102 and a periphery of the metal plate 100, and therefore, the metal plate must serve as a mechanical support as well as a thermal dissipator.
As the thickness of the metal plate 100 is reduced, the mechanical support provided by the metal plate 100 is lowered. Therefore, the metal plate has a lower limit, in thickness, of about 200 to 500 xcexcm, which is larger than the thickness of the semiconductor chip 102.
The semiconductor chip 102 also has a lower limit in thickness, so that there is a limit when reducing the thickness of semiconductor device by reducing the thickness of the semiconductor chip 102.
To achieve a further reduction in the weight and thickness of semiconductor devices, it is therefore desirable that an alternative member replaces the conventional metal plate to provide a good thermal dissipation and mechanical support while being lighter in weight and smaller in thickness than the metal plate.
The object of the present invention is to provide a semiconductor device having a heat dissipation plate which is lighter in weight and smaller in thickness than the conventional metal plate while ensuring a good thermal dissipation and mechanical support.
To achieve the object according to the present invention, there is provided a semiconductor device comprising:
a semiconductor chip having a back surface bonded to a lower surface of a heat dissipation plate having an area larger than that of the semiconductor chip;
a wiring board composed of a substrate having an upper surface with conductor patterns formed thereon, the conductor patterns having first ends connected to external connection terminals downwardly penetrating through, and protruding from a lower surface of, the substrate via through holes extending therethrough, the external connection terminals being disposed between a periphery of the semiconductor chip and a periphery of the wiring substrate;
the semiconductor chip and the wiring board being bonded to each other so that electrode terminals formed on an active surface of the semiconductor chip are electrically connected to second ends of the conductor patterns; and
the heat dissipation plate being composed of a fabric of carbon fibers and a resin impregnated in the fabric.
According to the present invention, the heat dissipation plate composed of a fabric of carbon fibers and a resin impregnated therein is lighter in weight than the conventional metal plate and provides good thermal dissipation and good mechanical support even when it has a reduced thickness. The carbon fibers of the heat dissipation plate have carbon chains oriented in the length direction thereof to provide a heat conduction coefficient as high as, or greater than, that of a metal of the conventional metal plate. The carbon fibers reinforce the heat dissipation plate to provide good mechanical strength even when the plate has a thickness as small as 100 xcexcm or less.
Thus, the heat dissipation plate of the present invention is lighter in weight than the conventional metal plate and provides a heat conduction comparable with, or greater than, that of the conventional metal plate, so that the semiconductor device of the present invention is lighter in weight and smaller in thickness than the conventional semiconductor device.
In a preferred embodiment, to provide a further reduction in weight and thickness, the wiring board comprises a flexible resin film and the second ends of the conductor patterns and the electrode terminals of the semiconductor chip are flip-chip bonded to each other.
In another preferred embodiment, to enable the amount of the impregnated resin to be as small as possible, the carbon fibers are carbon filaments and/or the fabric is a woven fabric of filamentary yarns each composed of a bundle of plural carbon filaments folded together.
In another preferred embodiment, the heat dissipation plate has sides containing cut ends of the carbon fibers and the cut ends are covered with a resin to prevent carbon particles from being generated from the cut surfaces.
In another preferred embodiment, the heat dissipation plate is composed of one piece of a woven fabric of carbon fibers and a resin impregnated in the woven fabric to provide a reduced thickness while ensuring an improved strength.
In another preferred embodiment, the heat dissipation plate is composed of a laminate of plural pieces of a woven fabric of carbon fibers and a resin impregnated in the fabric, the laminate having sides defined by cut surfaces formed by cutting in a direction of the lamination thereof and the cut surfaces being covered with a resin, to provide continuous carbon fibers, as a heat conduction path, through the thickness of the heat dissipation plate, thereby promoting heat dissipation.